*If* the X / Y deflection works as before, so calibrated time base steps
are still correct and calibrated vert amp steps, too, then you are
likely looking at a Z axis issue.
I'd recommend to check if the Z axis amplifier output is as expected. If
it is not, check the amplifier, if the amp is okay, check the Z axis logic.
If the amp output is okay, replace all HV caps and all diodes in the Z
axis DC restorer circuit.